1. Field of the Invention
The subject invention relates to integrated circuit attachment and removal apparatus, and more particularly to apparatus suitable for the attachment or removal of gull-wing-type quad pack integrated circuits from printed circuit boards.
2. Description of the Prior Art
In recent years, many devices and methods have been developed relating to the attachment of components to a printed circuit board. Examples of such joining processes include wave soldering, infrared radiant soldering, vapor phase soldering and hot bar soldering.
The impetus behind the development of such joining processes is in part due to the advent of multi-leaded electronic components. Over the past years, electronic components have advanced from components with two leads, like resistors, capacitors, etc., to integrated circuits with 10 to 100 or more leads. The leads on such integrated circuits typically emerge from the body of the IC from two or four sides of the device. On a "gull-wing" device, each lead extends outward from the side of the device, bends downward so as to form a knee, and then bends outward once again to form a foot suitable for attachment to a pad on the metallized surface of a printed circuit board.
Because of advances in technology that allow increasingly sophisticated circuitry to reside in a single IC, it is often necessary to use ICs having leads extending from all four sides. Such ICs are commonly referred to as "quad packs." The attachment and removal of quad packs has proven to be far more difficult than the attachment and removal of Dual-in-Line ICs.
Successful attachment of quad packs using current hot bar technology requires localized application of heat, sufficient to reflow the solder on the IC leads without reflowing the solder on nearby ICs. The successful removal of a quad pack requires that all of the leads be heated simultaneously and equally until all of the solder becomes liquid. The mass joining processes of wave soldering, infrared radiant soldering, and vapor phase soldering are not suitable for removal of quad packs because such processes do not allow for selectively melting the solder on the leads of the IC to be removed while not melting the solder joints of other components on the printed circuit board.
One prior art hot bar device provides a specifically-sized, closely toleranced monolithic cavity created from a single piece of metal. The monolithic cavity is placed over an IC such that the cavity surrounds and makes thermal contact with leads of the quad pack. Such monolithic cavity devices have two drawbacks. First, they are limited to use with ICs of a single size. Second, their fixed dimensions make it extremely difficult to accommodate the small but bothersome variations in dimensions of a particular IC that invariably occur from lot to lot. Such dimensional variations cause various problems. For example, if the so-called knee-to-knee dimensions of the leads of a gull-wing-type quad pack are too large, the device will not fit the cavity. If the knee-to-knee dimensions are too small, the loose fit will result in poor thermal contact between the heated walls of the cavity and the leads of the quad pack.
To overcome the inability of monolithic hot bar devices to accommodate the relatively small lot-to-lot variations in IC size, a prior art device having a base plate and four slidably adjustable heater bars situated orthogonally to one another has been provided. Each heater bar is machined to match the corresponding length of each side of a quad pack. This arrangement compensates for small variations in IC dimensions by providing tracks or slotted guides to allow for relatively minute adjustment of the heater bars. Because inward movement of one pair of the heater bars will interfere with the movement of the other pair of heater bars, the range of adjustment in such an arrangement is typically limited to .+-.0.015 inch. Although this adjustable heater bar arrangement provides a solution to the problem of lot variances in the dimensions of a particular device, it requires that a different set of heater bars be fabricated and maintained to accommodate each new device of different nominal dimensions. Additionally, inherent and costly delays are involved in procuring and changing the heater bars for different devices.